Intracellular recordings in the retina of the larval tiger salamander reveal two types of horizontal cell units. One of them (Type A), is hyperpolarized by illuminaton of any portion of its receptive field. The other (Type B), is not hyperpolarized by its surround unless the centre is simultaneously illuminted, stimulation of the surround alone resulting in either a small depolarization or virtually no response. Procion yellow injections suggested that both units may be just different parts of a single kind of horizontal cell -- the type B units representing the cell body, and the type A units, thick processes joined to the body by a fine fiber. The larger area and the properties of the receptive field of both types of units could be explained by assuming electrical connexions between units of the same type. It seems more likely, however, that the effect of the surround on type B units in due to a chemical synaptic inpingement from the type A units.